Mechanical characterization of coronary endoprostheses   (cf A9, A16, A17, C14, C15, C26, C27, C42, C50, C51, C52, C53). During the 90s, endovascular methods have started to stand as a major alternative to classical surgery. Stents allow to restore the initial caliber or arteries damaged by stenosing lesions. As practicians revealed problems possibly due to the mechanical comportment of the prosthesis itself, the production of several test benches seemed necessary to evaluate the mechanical properties of these materials while respecting the international standards being currently defined. The good long-term results of the "stenting" depend among others reasons on the hemocompatibility, on the resistance to crushing, on a limited "recoil" (elastic feedback), as well as on the difficulty of installation (path to the implementation area and deploy). Angioplasty is recommended in the treatment of vascular atheromateous stenosing lesions. This technology consists in inflating a small balloon inside of the artery in order do dilate the stenosed segment. Plates are then destroyed by fragmentation and crushing. However, after a such intervention, various phenomena can occur and involve a restenosis. On the one hand, the endothelium which covers the vascular lining is damaged, what favors the multiplication of cells from the subendothlial tissue, as well as the adhesion of the platelets, and thus the formation of thrombuses. On the other hand, two major lacks of parietal remolding are to be taken into account. The first one is the precocious elastic recoil which takes place in the 15 min following the angioplasty. It is only related to the mechanical properties of the vascular lining. The second one is a bad cicatrizing of the lining which is visible by a contraction of the artery which leads to a restriction of the vascular aperture. That is the reason why this technology is often accompanied by the implementation of an endoprosthesis (or stent) at the level of the lesion. After (or during) the angioplasty, the endoprosthesis is fitted in the dilated segment. Its structure allows to keep the vascular aperture open, and to avoid the inauspicious effects of the parietal remoulding, to prevent restenosis. Further on, by maximizing the size of the vessel, the impact of a fibromuscular growth inside the artery is minimized. The endoprosthesis only permits anyway to reduce the probability of restenosis after angioplasty, but not to totally avoid it. The ratio of restenosis after 6 months goes from about 35% for a angioplasty alone to 15-20% for an angioplasty accompanied by the implant of an endoprosthesis. Several parameters, such as the size or the shape of the stitches as well as the metal used, characterize the mechanical comportment of the endoprosthesis., and can have an influence on the restenosis. By now, many research works aim at linking the characteristics of endoprostheses to the 6-months rate of restenosis. When an endoprosthesis is installed in a sick artery with a view to mechanically sustaining it, it is important that the section of the blood flow (or artery aperture) within the endoprosthesis is of a dimension close to the initial section of flow of the sane artery so that the risks of restenosis are reduced. The goal of these studies lead in collaboration with Dr Paul Barragan (Beauregard Clinic, Marseille) is to predict the mechanical comportment of the endoprosthesis after its implementation. The test benches which were developed allow to present reliable evaluating systems of the mechanical characteristics of endoprostheses, as recommanded by the European norms. (EN 12006-3, January 1999), which shall be used by industrials whether in their demand of being CE labeled, or in their process of quality policy, or for research & development purpose. . Radial resistance to compression We evaluated the resistance to crushing of most of the coronary prostheses comercially available (27 models). The aim was to measure the distortion that the small caliber prostheses undergo, when they are submitted to external constraints such as those exerted by the arterial lining, and to evaluate their resistance to extreme forces. The results, which appeared in a publication at Cathetherisation and Cardiovascular Interventions (A16), shown that all the studied endoprostheses, while having each their own mechanical characteristics, were resistive enough to have a sane comportement after implementation. That is the reason why we focused our researches on another mechanical parameter of the stents, which is the intrinsic elastic recoil, which is of major importance, regarding the final diameter of the stented artery. In fact, an endoprosthesis dilated to a determined diameter naturally returns to an infirior diameter after deflation due to internal constraints. This recoil is more important when external constraints (even small) are applied by the lining to the endoprosthesis. . Elastic recoil This study aimed at determining in vitro the elastic recoil of 22 usual coronary endoprostheses dilated of 3.0 mm, using a device of optical measure of a great precision (SMARTSCOPE MVP 200; precision 1mm). A minimal recoil allows to adjust the final diameter of the stent to the nominal diameter of the artery; the more important the recoil, the more necessary it will be to over-dilate the endoprosthesis, and so the artery, with as a consequence an inauspicious impacting of the stent in the artery. Estimation of the in vitro elastic recoil when constrained on 22 coronary endoprostheses. The results clearly show that, depending on the design of the endoprosthesis (monofilament, laser cut tubular, hybrid), the important differences observed on the measured elastic recoil (between 2 and 18%), which can provoke, after a theoretical launch at a 3.0 mm diameter, a decrease of 0.5 mm on the final diameter. These results, which are currently being published (A17) have also pointed out a correlation between the elastic recoil and the restenosis rate after 6 months evaluated during several randomized clinical studies with various materials. . Evaluation of the trudging stress These tests were conducted with four commercial stents : Crossflex, CR153, PS153, PS154. For each model, six stents were successively tested. Over the four models of stents, only the Crossflex was delivered crimped on a dilatation catheter (CORDIS balloon). For the other models, we have conducted the tests with three stents crimped on a CORDIS balloon, and three stents crimped on a Bard SAMBA balloon. Five essential points emerge from that study : 1/ The results for the Crossflex stents were the same for tests separated by two weeks, which confirms the good repeativity of our tests. 2/ We came to a classification on grounds of their easiness to trudge into the tortuosities, which is, by order of growing difficulty : Crossflex, PS 153, CR 153, and PS 154 (this classification is confirmed by the practician). 3/ For a given stent, the more tortuous the artery is, the higher is the force to be applied to the stent for the passing through. 4/ The balloon on which the stent is crimped has a non-neglectable role : for whatever stent, the required force to have it pass through a tortuosity is always inferior when the balloon CORDIS is used in comparison with the balloon Bard SAMBA. 5/ The typical gap ever noticed in the results of the test lead with the PS154 stent is probably linked to the rigidity of this stent. Its rigidity causes the manner in which the stent arrives at the beginning of the tortuosity to have a significant influence on the intensity of the force to provide. Results of the tests of trackability in module 3